Current inertial sensing systems such as accelerometers, gravimeters and inclinometers are based on the relative displacement between an inertial mass and the base of the instrument when the base is subject to an external perturbation (vibration, modification of the “g” level, angle); and gyroscopes, which are another kind of inertial sensing system, are made of an inertial mass which is rotated about one of its axes of inertia and the measurement relies on the relative movement between the axis and the base of the instrument, or on the force generated by the axis on the base of the instrument, when the base is subject to an external movement.
The limitation of all those inertial sensing systems is mainly due to friction between the inertial mass and the base of the instrument.
Indeed this friction is responsible for imprecise measurement, of wear between the mechanical parts in contact, and it might also lead to failure due to mechanical fatigue.
In addition inertial sensing systems, such as seismometers in seismology or inclinometers in civil engineering, are often placed to monitor structures or machines and the power consumption of such systems is sometimes a critical factor.
Hence there is a need to make non-contact (contact less) inertial sensing systems with little energy consumption.
One way to answer this problem is to use diamagnetic levitation, which is the only stable passive (no energy input) levitation at room temperature: diamagnetic materials are repelled by magnetic fields. If the magnetic field is created by permanent magnets, a piece of diamagnetic material can thus be passively and stably levitated.
In the U.S. Pat. No. 3,831,287 a tiltmeter is designed using diamagnetic levitation but without axial contact-less stabilization of the diamagnetic inertial mass. The diamagnetic force exerted over the inertial mass is created by a 1D arrangement of large horseshoe magnets resulting in an unstable levitation in the axial direction.
In the U.S. Pat. No. 5,396,136 an array of permanent magnets is levitated by magnetic interaction with a diamagnetic material (pyrolitic graphite).
In such a configuration magnets are heavier than graphite for the same volume of material, and diamagnetic materials (such as pyrolitic graphite) is much more expensive than magnets for the same volume of material (or for the same weight). In addition such a stabilisation, using a bowl shape diamagnetic material, is not active and would not, if used as a sensor, behave with the high sensitivity of a force balance inertial sensing system such as the ones of the present invention.
Other prior art references are listed below:    R. Moser, J. Sandtner, H. Bleuler, Diamagnetic Suspension System for Small Rotors, Journal of Micromechatronics, Vol. 1, No2, 2001.    R. Moser, J. Sandtner, H. Bleuler, Diamagnetic Suspension Assisted by Active Electrostatic Actuators, 6th International Symposium on Magnetic Suspension Technology, Oct. 6, 2001.    R. Moser, Y-J. Regamey, H. Bleuler, Passive Diamagnetic Levitation for Flywheels, ISMB, Sep. 24, 2002.    R. Moser, F. Barrot, H. Bleuler, Optimization of Two-Dimensionnal Permanent Magnet Arrays for Diamagnetic Levitation, MAGLEV, Sep. 9, 2002.    Science Toys, Levitating Pyrolitic Graphite: http://www.scitoys.com/scitoys/scitoys/magnets/pyrolitic graphite.html July 2002.